The
ends are removed by a saw, and the bones are steeped in a 1% brine
solution for three to four days, in order to separate the fibrous
matter. The bones are now heated with water, and allowed to simmer for
about six hours. This removes a part of the fat and gelatinous matter;
the former rises as a scum, the latter passes into solution, and the
bones remain sufficiently firm to be worked up by the lathe, &c. The
fat is skimmed off, and, after bleaching, reappears as a component of
fine soaps, or, if unbleached, the oil is expressed and is used as an
adulterant of other oils, while the stearine or solid matter goes to
the candle-maker; the gelatinous water is used (after filtration) for
making size for cardboard boxes; while the bones are scrubbed, dried,
and then transferred to the bone-worker.

The glue-worker first removes the fat, which is supplied to the soap
and candle trades; the bones are now treated for glue (q.v.); and
the residue is worked up for manures, &c. These residues are ground to
a fine or coarse meal, and supplied either directly as a fertilizer or
treated with sulphuric acid to form the more soluble superphosphates,
which are more readily assimilated by growing plants. In some places,
especially South America, the residues are burned in a retort to a
white ash, the "bone-ash" of commerce, which contains some 70-80% of
tricalcium phosphate, and is much used as a manure, and in the
manufacture of high-grade superphosphates. In the gelatin industry
(see GELATIN) the mineral matter has to be recovered from its solution
in hydrochloric acid. To effect this, the liquors are freed from
suspended matter by filtration, and then run into vats where they are
mixed with milk of lime, or some similar neutralizer. The slightly
soluble bicalcium phosphate, CaHPO4, is first precipitated, which,
with more lime, gives ordinary tricalcium phosphate, Ca3(PO4)2. The
contents of the vats are filter-pressed, and the cakes dried on
plates supported on racks in heated chambers. This product is a very
valuable manure, and is also used in the manufacture of phosphorus.

Instead of extracting all the gelatinous matter from degreased bones,
the practice of extracting about one half and carbonizing the residue
is frequently adopted. The bones are heated in horizontal cast-iron
retorts, holding about 5 cwt., and the operation occupies about twelve
to thirte